Hide king wearing something wicked (4)
I believe the answer is:
skin
'hide' is the definition.
(a hide is an animal skin)
'king wearing something wicked' is the wordplay.
'king' becomes 'K' (chess abbreviation).
'wearing' indicates putting letters inside.
'something wicked' becomes 'sin' (sin is wicked).
'k' put into 'sin' is 'SKIN'.
(Other definitions for skin that I've seen before include "External membrane of body" , "Hide - flay" , "Dermis" , "Surface layer" , "Outer layer of a fruit or vegetable" .)